It does tie it self to a PC. If you upgrade enough of a PC, you will have to call M$. How much, I don't know. If you change just hard drives, then you probably wouldn't need to; but if you change your hard drive, video card, sound card, you might have to. M$ is the only ones who really know, I think. I would guess that changing motherboards would be enough to require re-activation, but I could be wrong.